Frequency modulation



July 3, 1934. J. w. coNKLlN FREQUENCY MODULATION Filed Dec. 17, 1952 I2 Sheets-Sheet l W m o, M

INVENTOR- JAMES W. CONKLN BY Y `A'TT M July 3, 1934. J. W. coNKLlN 1,965,332

FREQUENCY MODULATION INVENTOR- JAMES w. coNKLlN Patented July 3, 1.934

Unirse STATES '1,965,332 FREQUENCY MODULATION James W, Conklin, Rocky Point, N. Y., assigno to Radio'CorJoration of America, a corporation of Delaware Application December 17', 1932, 'serial No. 647,735

3 Claims.

This invention relates to a system for producing frequency modulated waves and has as a broad object, the frequency modulation of the magnetron type of oscillator. I Yhave found that by varying the anode potential, field strength or filament temperature of a magnetron oscillator, in addition to a large amount of amplitude modulation, there is also present a frequency modulated component. The frequency modulated waves, broadly, according to my presentinvention, may be transmitted to the exclusion of the amplitude modulated component by eliminating the latter by means of suitable limiting devices following the modulated magnetron oscillator.

Moreover, during my experiments with oscillators of the magnetron type, I have found that, with increasing strength of magnetic field, or, with increasing strength of anode or cold electrode potential, there is a certain range of operating conditions at which variations in cold electrode potential or magnetic field strength produce substantially no amplitude variation. I-I'owever, in this constant amplitude range, I have found that the frequency of oscillation varies with the applied cold electrode potentials or magnetic field strength. According to the preferred form of my present invention, I make provisions for utilizing this phenomenon whereby the heretofore required limiter may be eliminated, if desired, or if one is used, it will only be required to exercise its smoothing action throughout a much smaller range of potentials thereby offering the advantage that the limiter will enjoy a much longer life.

Further understanding of my present invention both as to its mode of operation and structural organization may best be had by referring to the accompanying drawings, wherein,

Figures 1 and 2 are curves explanatory of my present invention; and,

Figures 3 to 8 inclusive are wiring diagrams of various magnetron circuits whereby substantially pure frequency modulated energy may be lderived from a magnetron oscillator.

If a magnetron oscillator such as a magnetron 2 of Figure 3 having a relatively cold or anode electrode 4, symmetrical and concentric with its filament or cathode 6, a magnetic field coil 8 and -a source of anode potential 10, has its cold electrode or anode potential varied or the applied magnetic field strength varied, the amplitude of oscillations generated will follow a curve somewhat as illustrated in Figure 1. I have found that over the range AB of field strength or plate (ci. ris-171) potential wherein the amplitudel of oscillations remain substantially constant, the frequency of oscillations generated Varies substantially linearly as indicated in Figure 2. According to the preferred forms of my present invention, it is over this range that I operate a magnetron oscillator in order to obtain an output which is purely frequency modulated and substantially free of' amplitude modulation or variation.

In Figure 3, the plate potential of the magnetron oscillator 2 is varied as follows. Modulating potentials, of relatively low frequency, such as keyed signals, television signals, or audio frequency tones, are applied through a transformer 12 to the vacuum tube amplifier 14. The anode potential fed to the plate 4 through impedance 16, which may be a resistor or an inductance, is so adjusted as is also the current iiowing through the eld coil 8, that normally the magnetronv oscillator 2 operates at point C in Figures 1 and 2. By controlling the potential appliedY through transformer 12, or, by adjusting the tap on input resistor 22, the modulating potentialsapplied to the anode 4 through high frequency choke coil 24 may be kept within the values AB of Figures l and 2. Hence, in accordance with what has gone on before, the oscillatory energy in the output circuit 26 which output circuit is blocked off from anode potential by means of condenser 28, will be modulated purely in frequency, and this energy may be applied inductively as illustrated to any suitable radiating antenna 30.

In the event that impedance 16 is in the form of a resistor, variable current ows through modulator tube 14 will, of course, vary the potential on the plate 4. In the event that the impedance is made in the form of an inductance not only will the potential vary, but also the current or energy fed to the magnetron 2 will vary but in any event, the results will be the same, namely, a substantially constant amplitude frequency modulated wave.

If desired, of course, frequency multipliers and/or ampliers and/or limiters may be inserted between the output circuit 26 having inductance and capacity and the nal utilization circuit 30.

In the alternative, as shown in Figure 4, the output of modulator tube 14 may be utilized to vary the magnetic eld strength produced by coil 8 of the magnetron 2. As illustrated in Figure 4, Voltage variations, current variations or the combination of both within the limits AB are applied to the solenoid 8 of magnetron 2. Consequently, in the output circuit 30 blocked off from the magnetron electrodes by means of stopping or by-passing condensers 28 there Will appear frequency modulated electrical waves Which in turn may bev fed through by-passing con- Y densers 32 and transmission line 34 to the half Wave linear radiating antenna 36. Here also, if desired, frequency multipliers and/or amplifiers and/ or limiters may be inserted between the output circuit 30 and the nal utilization circuit 36.

Rather than directly vary the strength of the current flowing in the main eld coil 8, an auX- iliary coil 38 as shown in Figure 5, may be provided. Modulating currents owing through the auxiliary coil will, of course, add to or detract from the strength of the main field supply, adjustments being made preferably so as not to exceed the operating limits AB of Figures 1 and 2.

In the further alternative, the modulating signal input may be applied in series with the main eld supply by means of a serially connected transformer 40 as illustrated in Figure 6, or, the modulating potentials may be similarly serially applied to the cold electrode or anode 4 as illustrated in Figure 7.

It is to be clearly understood, however, that my present invention is not limited to magnetrons having a single cold electrode. In Figure 8 I have illustrated a magnetron having a split anode comprising cylindrical segments 42, 44 connected in phase opposition by tunable output circuit 46 supplied through a secondary of modulation transformer 48 with positive potential. A magnetic field is applied to the electrons iiowing from the lamentary or linear coaxial cathode 6 to the anode segments, by means of solenoid 50 Wrapped about the glass envelope of the tube Which, for the sake of clarity has not been illustrated. By varying resistance 52 and by suitably varying the strength of anode potential applied through lead 54, the tube is caused to operate at preferably, point C of Figures 1 and 2. Modulating potentials may be applied from a source 56 through variable modulation transformer 58 to the solenoid 50 and in addition, if desired, through transformer 48 to the anodes. The transformers 48, 58 may be adjusted in polarity so that their effects either add or subtract, but in any event, adjustments should be made so that the operating range falls Within the limits AB illustrated in Figures 1 and 2. Obviously, if desired, either of the transformers 48, 58 may be eliminated.

To improve operation, if desired further, the solenoid A may be electrostatically shielded from the tube and oscillating circuits as described more fully in the copending application of Harold O. Peterson, Serial Number 647,725, filed December 17, 1932.

Having thus described my invention, what I claim is:

1. The method of operating electrical apparatus comprising an electron discharge device having within an hermetically sealed container and electron emitting cathode, and a cold electrode spaced from said cathode; a magnetic circuit for applying a magnetic field to electrons flowing within said container, a circuit adapted to vary the potential on said cold electrode; and, a 100 modulation circuit coupled to one of said aforementioned circuits; which includes the steps of adjusting either or both of said magnetic and potential circuits so that over a predetermined range of potentials fed to either circuit oscillal05 tions of constant amplitude are generated, and, the step of adjusting said modulating circuit so that potentials fed from it into one of said other circuits lie within said constant amplitude range whereby the oscillations generated by said de- 110 vice vary substantially only in frequency with variations in modulating potentials.

2. The method as claimed in claim 1 characterized by the fact that the modulating potentials are applied to the cold electrode circuit.

3. The method as claimed in claim 1 characterized by the fact that the modulating potentials are applied to the magnetic circuit.

JAMES W. CONKLIN. 

